The present invention is related to low loss optic elements such as windows or lenses for use in equipment such as lasers. In the prior art it has been known to use Brewster windows in laser application. The Brewster window is a glass window used at opposite ends of some gas lasers to transmit one polarization of the laser output beam without loss. Previous Brewster window designs have been continuous sheets of glass. Small mismatches in expansion coefficients of the window and of the laser body to which the window is fastened result in stresses in the glass as the temperature changes. Such stresses make the glass window birefringent which increases surface reflectance losses and reduces power output from the laser. Birefringence also provides a retardance mechanism which creates elliptically polarized light from plane polarized light. When the laser is used in laser gyro applications, such elliptically polarized light results in a bias sensitivity to magnetic fields and performance degradation.
In the present invention the Brewster window has a novel structure in that a plurality of circular or curved grooves are formed in the window to isolate stresses from reaching the important window central region used for light beam transmission. The plurality of grooves effectively form a resilient or spring-like zone between the area used to attach the window and the central area used for light beam transmission. Differential (e.g. thermal) motion generated in the peripheral mounting area is stress-decoupled or absorbed in the spring-like region and thereby significantly reduces or eliminates stresses transmitted to the central region of the window.